The invention relates to a microwave antenna with a substrate with at least one resonant conductor track structure, designed in particular for mobile dual-band or multiband telecommunication devices such as mobile and cellular telephones, as well as for devices which communicate in accordance with the Bluetooth standard. The invention further relates to a printed circuit board with such an antenna and to a telecommunication device with such an antenna.
Electromagnetic waves in the microwave range are used in mobile telecommunication for the transmission of information. The GSM mobile telephone standard is used exclusively in Europe and in a majority of the rest of the world for cellular systems. Within this GSM standard there are several frequency bands in which the communication may take place: on the one hand from 880 to 960 MHz (the so-called GSM900) and on the other hand from 1710 to 1880 MHz (the so-called GSM 1800 or DCS). A third band, which is mainly used in the USA, uses frequencies from 1850 to 1990 MHz (GSM1900 or PCS).
Usually a network service provider will offer his services in only one of these frequency bands. Increasingly, however, mobile telephones are constructed such that they can operate in several frequency bands so as to safeguard a wide covering range and to provide a universal operation possibility for the mobile telephones in any location whatsoever, independently of the conditions prevailing locally and the networks operated locally. These mobile telephones are also referred to as dual-band or multiband mobile telephones. A precondition for this is, however, that the antenna of such a mobile telephone is capable of transmitting and receiving electromagnetic waves in the respective two or more frequency bands.
A further standard which was recently developed is the so-called Bluetooth standard (BT) for which the frequency range from 2.4 to 2.48 GHz is reserved and which serves for the exchange of data between, for example, mobile telephones and other electronic devices such as, for example, computers, other mobile telephones, etc.
Furthermore, the market shows a strong trend towards miniaturization of the devices. This results in the wish also to reduce the components for the mobile communication, i.e. the electronic components, in size. The antenna types used at present in mobile telephones, which are usually wire antennas, have substantial disadvantages in this respect, because they are comparatively large. They project from the mobile telephones, may readily break off, may come into undesirable eye contact with the user, and also stand in the way of an aesthetic design. Increasingly, moreover, an undesirable microwave irradiation of the user by the mobile telephone has become a subject of public discussion. A major portion of the emitted radiation power may be absorbed in the user""s head in the case of wire antennas which project from the mobile telephone.
Surface mounting (with SMDs or surface mounted devices), i.e. the planar soldering of electronic components onto a PCB or printed circuit board by means of a wave soldering bath or a reflow soldering process, has become common practice in the technical realization of modem digital electronic devices. The antennas used until now, however, are not suitable for this mounting technology, because they often can only be provided on the printed circuit board of the mobile telephone by means of special supports, while also the supply of electromagnetic power is only possible by means of special supply/support members such as pins or the like. This causes undesirable mounting steps, quality problems, and additional cost in production.
Efforts are made to come to terms with these very different requirements and problems through an optimized antenna design. It should be taken into account here that in particular the structure of the antenna is more strongly dependent on the desired frequency range and the application of the relevant electronic device than that of any other HF component, because the antenna is a resonant component which is to be attuned to the respective operating frequency range. In general, conventional wire antennas are used for transmitting and receiving the desired information. Certain physical lengths are absolutely necessary if good radiation and reception conditions are to be achieved for this type of antennas. So-called xcex/2 dipole antennas (xcex=wavelength of the signal in the open space) were found to be particularly advantageous in this respect, which antennas are formed by two wires, each xcex/4 long, which are mutually rotated through 180xc2x0. Since these dipole antennas are too large for many applications, however, in particular for mobile telecommunication (the wavelength for the GSM900 range is, for example, approximately 32 cm), alternative antenna structures are utilized. A widely used antenna in particular for the mobile telecommunication bands is the so-called xcex/4 monopole which is formed by a wire with a length of xcex/4. The radiation behavior of this antenna is acceptable while at the same time its physical length (approximately 8 cm for GSM900) is satisfactory. This type of antenna in addition is characterized by a great impedance and radiation bandwidth, so that it can also be used in systems which require a comparatively great bandwidth such as, for example, mobile telephone systems. To achieve an optimum power adaptation to 50 xcexa9, a passive electrical adaptation is used for this type of antenna (as is also the case for most xcex/2 dipoles). This adaptation is usually formed by a combination of at least one coil and a capacitance, which adapts the input impedance different from 50 xcexa9 to the connected 50 xcexa9 components by means of a suitable dimensioning.
A further possibility is to achieve a miniaturization of this antenna through the use of a medium having a dielectric constant ∈r greater than 1, because the wavelength is reduced by a factor 1/⊂∈r in such a medium.
An antenna of this type comprises a solid block (substrate) of a dielectric material. A metal conductor track is printed on this block. This conductor track is capable of radiating energy in the form of electromagnetic waves upon reaching an electromagnetic resonance. The values of the resonance frequencies depend on the dimensions of the printed conductor tracks and the value of the dielectric constant of the block. The values of the individual resonance frequencies drop with an increase in the length of the conductor track and with an increase in the value of the dielectric constant.
To achieve a high degree of miniaturization of the antenna, accordingly, a material with a high dielectric constant will be chosen, and the mode with the lowest frequency will be chosen from the resonance spectrum. This mode is designated the base or fundamental mode, the next higher mode with respect to the resonance frequency is denoted the first harmonic. Such an antenna is also referred to as printed wire antenna. The bandwidth of such a known antenna is satisfactory in the case of resonance frequencies which lie in the region covered by the GSM standard only for achieving a full coverage of one of the frequency bands of the GSM standard. The dual-band or multiband applications mentioned above are accordingly not possible here.
It is an object of the invention, therefore, to provide a microwave antenna which is suitable for said dual-band or multiband applications and which has dimensions which are as small as possible.
Furthermore, a microwave antenna is to be provided which can be mounted by the SMD technology through planar soldering and contacting on the conductor tracksxe2x80x94possibly together with other components of the printed circuit boardxe2x80x94without additional supports (pins) for the supply of the electromagnetic power being necessary.
The invention also has for its object to provide a microwave antenna whose resonance frequencies can be individually adjusted without changes in the basic antenna design such that they can be attuned to a given constructional situation.
Finally, a microwave antenna is to be provided whose input impedance can also be individually adapted to a given constructional situation.
To achieve these objects, a microwave antenna is provided with a substrate having at least one resonant conductor track structure, characterized in accordance with claim 1 in that a first conductor track structure is formed by at least a first and a second conductor portion, which extend in a substantially meandering shape, and in that the two conductor portions have a distance that determines the frequency distance between the first resonance frequency of the fundamental mode and the second resonance frequency for the first harmonic of the fundamental mode can be adjusted through a change in the distance between the two conductor portions.
A particular advantage of this solution is that the frequency of the fundamental mode can be adjusted by means of the total length of the conductor track structure, and the frequency distance between the fundamental mode and the first harmonic can be adjusted by means of said distance such that the antenna can be operated as a dual-band antenna in the GSM900 and GSM1800 bands.
The dependent claims define advantageous further embodiments of the invention.
The embodiments of claims 2 and 3 have the advantage that the frequency distance can be adjusted even better.
The embodiment of claim 4 has the advantage that a surface mounting of the antenna together with other components on a printed circuit board is possible, so that the manufacture can be substantially simplified and quickened.
The embodiment of claim 5 renders possible an independent adjustment of the frequency of the fundamental mode or the first harmonic without the other one of these two frequencies being appreciably influenced.
The embodiment of claim 6 has the advantage that the antenna can even be operated in three frequency bands, while according to claim 7 a supply through a joint feed terminal is possible.
A tuning of the individual resonance frequencies of this three-band antenna can be carried out in the embodiments of claims 8 and 9.